1. Field of the Invention
The present invention relates to a focus state detecting device for use in a camera or the like.
2. Related Background Art
A focus state detecting device having two pairs of photoelectric sensor arrays for detecting displacement in the light image in two directions on a plane perpendicular to the optical axis is already known in the Japanese Laid-open Patent 62-173413. Such known device will be explained in the following with reference to FIG. 1.
A focus state detecting optical system is provided with a viewing field mask 2101 positioned in the vicinity of a focus state detecting plane; a field lens 2102; a diaphragm plate 2103 having two pairs of apertures; and a re-imaging lens 2104, and is composed of an optical system for guiding light fluxes having passed spatially different areas 2103a, 2103b to a pair of photoelectric sensor arrays 2105a, 2105b, and another optical system for guiding the light fluxes having passed spatially different areas 2103c, 2103d, which are different from those mentioned above, to another pair of photoelectric sensor arrays 2105c, 2105d. The first pair of photoelectric sensor arrays 2105a, 2105b is positioned perpendicular to the latter pair of photoelectric sensor arrays 2105c, 2105d.
Though the above-mentioned Japanese Laid-open Patent 62-173413 does not disclose the arrangement of circuits related to the driving of the photoelectric sensor arrays, the related circuits in fact have to be placed on the substrate bearing the photoelectric sensor arrays, so that a space for the circuits has to be provided on the substrate. This fact limits the arrangement of the photoelectric sensor arrays, thus resulting in a drawback of limitation in the light receiving area or focus state detecting area.
The Japanese Laid-open patent 62-212611 discloses, as in the Japanese Laid-open Patent 62-173413, a device for detecting the displacement of the image in two directions on a plane perpendicular to the optical axis of the optical system. The Japanese Laid-open Patent 62-212611 discloses the arrangement of the related circuits on the substrate bearing the photoelectric sensor arrays as shown in FIG. 2, in which the charges accumulated in the arrays PD1, PD4 are transferred through a common shift register CCD1 to an output stage OS1, while those accumulated in the arrays PD2, PD3 are transferred through a common shift register CCD2 to an output stage OS2, and transfer gates G1, G2, G3, G4 are provided to transfer the charges accumulated in the arrays to the neighboring shift registers. The arrays PD1 and PD3 are paired to detect the image displacement in one direction, while the arrays PD2 and PD4 are paired to detect that in another direction. Thus the output of the array PD1 is compared with that of PD3, and the output of the array PD2 is compared with that of PD4. However, since the arrays PD1 and PD3 have different output stages, the output signal levels from the output stages may be different even when the object has uniform luminosity, thus giving rise to a deteriorated precision of detection.